Split Serial forking scenario into its own section

[kyzer-davis]

Remove:

*  A similar scenario was brought up in Appendix A of [RFC4568]         
      "Scenario B" and "Problem 3" of the summary within this section.

Add:

Serial Forking Case:

{: spacing="compact"}
- {{RFC4568}} itself cites a problematic scenario in their own Appendix A, Scenario B, Problem 3 where a ROC out of sync scenario could occur.
- The proposed solution for problem 3 involves a method to convey the ROC however known the problem; the authors still did not include this in the base SDP Security specification.